Early Repayment Calculator: Estimate Interest Savings

This early repayment calculator estimates how much interest you would pay if a fixed-rate loan were repaid early with equal monthly payments. Enter the loan balance, annual APR, original term, and the month you plan to make the final payment; the results show the regular payment, estimated balance at that point, and interest avoided compared with paying for the full term.

Formula

The calculator first finds the level monthly payment, using a fixed monthly rate and the original loan term. It then estimates the remaining balance after the selected number of payments. Interest avoided is the interest that would have been paid over the full scheduled term minus the interest included in payments made before early payoff.

• Monthly payment: M = round[P × r / (1 − (1 + r)^−N), 2].
• Balance after k payments: B = max[0, P(1 + r)^k − M((1 + r)^k − 1) / r].
• Scheduled total interest: I_full = M × N − P.
• Interest paid before payoff: I_early = M × k − (P − B).
• Estimated interest avoided: S = I_full − I_early.

P is the starting loan amount in dollars; APR is the annual percentage rate; r = APR / 1,200 is the monthly rate as a decimal; N is the original term in months; k is the number of regular payments made before payoff; M is the monthly payment in dollars; B is the estimated balance in dollars. The expression max(0, …) prevents a negative displayed balance if the selected month is beyond the loan’s scheduled term. The payment output is rounded to cents, and subsequent estimates use that rounded payment.

Worked Example

With the default inputs, the loan amount is $20,000, APR is 8%, the term is five years (60 months), and 24 payments are made before early payoff.

1. Monthly rate: r = 8 / 1,200 = 0.0066667.
2. Monthly payment: M = round[20,000 × 0.0066667 / (1 − (1.0066667)⁻⁶⁰), 2] = $405.53.
3. Balance after 24 payments: B = 20,000(1.0066667)²⁴ − 405.53 × [(1.0066667)²⁴ − 1] / 0.0066667 = $12,835.58.
4. Interest over the full schedule: 405.53 × 60 − 20,000 = $4,331.80.
5. Interest in the first 24 payments: 405.53 × 24 − (20,000 − 12,835.58) = $2,568.30.
6. Estimated interest avoided: 4,331.80 − 2,568.30 = $1,763.50.

Assumptions

• The interest rate is fixed for the calculation period.
• Payments are equal, made monthly, and applied at the end of each month.
• Interest is modelled monthly at APR divided by 12.
• The calculation does not include payoff fees, taxes, insurance, PMI, escrow, or other charges; the loan has no separate payment changes or irregular payment dates.
• The displayed early-payoff balance is an estimate, not necessarily the lender’s payoff quote.

What Early Repayment Means

Early repayment means clearing some or all of a loan principal before the original repayment schedule ends. It may happen through extra amounts added to regular installments, a lump-sum payment, or a final payoff of the remaining balance. Paying principal down earlier generally reduces the amount on which later interest is calculated in a standard amortizing loan, but the amount saved depends on the contract’s calculation method, timing, and charges.

This tool models a particular case: regular monthly payments continue through month k, then the remaining balance is paid off. It does not model a partial lump-sum payment while installments continue. For that situation, you would need to recalculate the payment or balance after the extra principal is applied.

How to Use and Read the Results

Use the amount currently owed as the loan amount only if the loan is at the start of its schedule. If you have already made payments, entering the original amount and full original term describes the whole loan from its beginning; to estimate from today, the calculator would need the current principal and remaining term instead. APR and term should match the figures used in the loan’s payment schedule.

• Set “Payments made before early payoff” to the number of regular payments expected before the final payoff. For example, 24 means the model makes 24 monthly payments, then settles the balance.
• Read “Balance after selected payments” as estimated principal still owed immediately after those payments, before any additional payoff charges.
• “Interest avoided” compares interest through the scheduled end with interest through the selected payoff month. It is not the amount of the payoff itself.
• For an immediate payoff estimate, enter zero payments. The model then shows the original principal as the balance and zero interest paid before payoff.

A loan’s actual payoff amount can differ from its statement balance because interest may accrue between payment dates or charges may apply. Ask the servicer or lender for a dated payoff quote and confirm how an extra payment is credited. Some contracts may apply additional money to future installments rather than immediately reducing principal unless the payment is designated appropriately.

Limits, Costs, and Common Misunderstandings

The estimate assumes a constant APR, fixed installment, and monthly amortization. It is not a universal early-repayment formula: variable rates, daily interest calculations, interest-only periods, balloon payments, skipped payments, payment holidays, and irregular dates change the result. Small differences can also arise from the lender’s rounding rules and the exact day funds are received.

Interest avoided is not necessarily equal to the financial benefit of paying early. A payoff charge or other cost can reduce the net difference, while the money used for repayment may have other uses. This calculator does not compare those alternatives or account for tax treatment. It also does not establish whether a fee is permitted or applicable; check the loan documents and obtain the actual figures from the lender. It is an estimate for education, not financial advice.

Frequently Asked Questions

Does early repayment always save interest?
For a standard amortizing loan with interest based on the outstanding principal, paying principal sooner usually reduces later interest. Actual savings can be affected by charges, payment timing, and contract terms, so check a dated payoff quote.

Is the early payoff balance the same as the payoff amount?
Not necessarily. The calculator estimates principal after scheduled payments. A lender’s payoff quote may include accrued interest through a specified date and applicable charges.

What should I enter if I have already been paying the loan?
For a forward-looking estimate, enter the current principal balance and the remaining term, rather than the original amount and original term. This calculator does not separately account for the history of earlier payments.

Can I use this for an extra lump-sum payment?
Not directly. It models continuing regular payments followed by full payoff. A partial lump sum followed by revised installments needs a balance or payment calculation that includes the lump sum and its date.

Why might my lender’s numbers differ?
Lenders may calculate interest daily, use different rounding, receive payments on different dates, or include charges not represented here. The lender’s disclosure and dated payoff quote provide the figures for the actual account.

The result is an estimate, and the lender’s disclosure gives the exact figures.

Related

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
in k | Payments made before early payoff | months | 24 | 0 | 600
out bal | Balance after selected payments | $ | max(0, p * (1 + apr / 1200) ^ k - pmt * ((1 + apr / 1200) ^ k - 1) / (apr / 1200)) | 2
out full | Total interest if paid on schedule | $ | pmt * yrs * 12 - p | 2
out paid | Interest paid before early payoff | $ | pmt * k - (p - bal) | 2
out save | Estimated interest avoided | $ | full - paid | 2
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2